This invention relates to motor protectors and more particularly to protectors for split-phase motors in which the usual motor starting switch is utilized to effect masking of the current-biasing or self-heating effects of motor current through the protector's thermostatic element during running mode operation.
Motor protectors of many different types have long been used to protect motors from damaging overtemperature conditions such as would be caused by sudden massive overloads due to a locked rotor or a long-term overcurrent condition where the temperature of the motor eventually rises to a level that would damage the motor if continued, e.g., an ultimate trip current condition. Numerous approaches have been taken with varying degrees of success to provide protectors which will satisfactorily protect against these two quite different types of motor overload conditions. At the same time, motor standards have been uprated and cost economies in motor design have been made so that all motor materials must work harder. This has imposed increasingly stringent requirements and constraints on the motor protector designer and manufacturer in producing improved performance protectors at minimal expense and has hampered further economies in motor design and construction.